The present invention relates to improvements in electronic weighing devices such as scales, and in particular to an improved switching apparatus and an improved coded disc reading apparatus for such devices.
Electronic weighing devices such as digital scales employing optically coded discs are known to the art. One type of such scale employs a scale mechanism which rotates an optically coded disc to a position which corresponds to the magnitude of the vertical forces applied to the scale mechanism. A reading mechanism is provided to sense optically coded indicia on the disc to measure the position of the disc and thereby the applied vertical force.
One recurring problem of the prior art relates to the manner in which the reading mechanism is switched on and off. It is often preferable to use batteries contained in the scale to power the reading mechanism, and in order to extend battery life it is important to de-energize the reading mechanism when not in use.
One approach to this problem is to use a kick-bar on the scale to allow a user to activate the reading mechanism manually. U.S. Pat. No. 4,082,153 shows one such device. An important disadvantage of this approach is that the scale does not automatically energize upon use. Instead, an active decision by the user to turn on the scale is required.
A second approach is to employ an automatic switch which works off of the scale mechanism and is therefore responsive to applied vertical forces on the scale. This approach provides the advantage of automatic operation. However, since the switch works off of the scale mechanism, it can on occasion interfere with the proper operation of the scale mechanism. Furthermore, additional means must be provided to energize the scale for zero set operations, when no vertical forces are applied to the scale mechanism. In the past, such additional means have included manually operated switches, which may be relatively inaccessible. In addition, this approach generally requires that the user be instructed as to how to find and manipulate this additional means.
An additional aspect of the prior art relates to light guides which direct light from a source such as a light bulb or LED to the optically coded disc for use in sensing the optical indicia on the disc. In the past, such light guides have been designed to direct light onto a radius of the disc, and the associated photosensors have been aligned along this radius as well. This approach results in a bulky and elongated light guide which extends from a radius to a point beyond the periphery of the disc. Such bulky light guides can result in mounting structures which are larger and therefore more expensive to manufacture than necessary.